About 250 protesters demonstrating in memory of Eric Garner and Mike Brown climbed up flagpoles at the headquarters of the Oakland, California, Police Department on Monday, leading to the arrests of 13 people, NBC Bay Area reported. About 250 people participated in the protest, while others blocked city roads and chained police headquarters shut, according to the Associated Press.

The protests, which started at 7:30 a.m. PST, were held to express frustration over the lack of indictments against the white police officers who killed Garner in Staten Island, New York, in July and Brown in Ferguson, Missouri, in August. Organizers told NBC Bay Area they wanted the protests to last for four hours and 28 minutes to represent the time Brown, 18, lay dead in the street before his body was recovered and 28 minutes to symbolize that a black man is killed every 28 hours in the United States.

While the protesters were cleared by noon, according to the Bay Area Solidarity Action Team, some of those involved demonstrated for longer. Laura Anthony, a reporter for San Francisco ABC affiliate KGO, tweeted pictures around 12:20 p.m. PST of a person who climbed the flagpole at Oakland police headquarters:

Felicia Gustin of the Bay Area Solidarity Action Team, self-described as a group of whites for racial justice, said in a press release that the Brown and Garner deaths represent “a moral crisis.” “Silence is violence,” she said. “The abusive treatment of people of color by the police is a moral crisis for our country and our city, and we cannot turn a blind eye any longer. It is time for white people to join with black communities to end the war on black people.”

Besides the demonstration at the Oakland police HQ, protesters also blocked two roads in downtown Oakland near the building, according to the AP.

“We fight for justice for every single black life that has passed at the hands of police,” organizer Dierdre Smith told NBC News Bay Area. "But we must also stand up and shut down for the black and breathing who are at risk of the same fate.”